Error - 21206

Invalid SendDigits

You attempted to initiate an outbound phone call, and you included a SendDigits parameter that wasn't valid. SendDigits is optional, and specifies that Twilio should simulate sending keypad digits when the party answers. It is useful for navigating a phone tree, reaching an extension or entering a password in a voicemail system. SendDigits may contain numbers, the # and * characters, as well as the "w" character to "wait" for half a second.